Infections

In agriculture, people work close to water, animals, crops, natural fertilizers, and the soil, all of which serve to carry infectious diseases that can infect the skin. Persons with immunological disease, malnutrition, diabetes, and severe systemic disease are at risk for any kind of a infectious disease.

Bacterial Infections Staphylococci and Streptococci

These gram-positive bacteria cause infection through contamination of cuts, burns, puncture wounds, and abrasions. All occupations are at risk, but those who work with meat are found to be particularly affected. Treatment is cleansing the wound and oral antibiotics (51).

Anthrax

Anthrax is associated with people who handle wool, hides, or sheep. Bacillus anthracis is a gram-positive, spore-forming rod distributed worldwide. Animals are infected by ingestion of spores while feeding on contaminated soil. The spores can survive for years in the soil or in contaminated animal material, such as lamb's wool (51-53).

Infection in humans typically occurs at sites of skin trauma. The lesion starts as a painless, pruritic papule that vesiculates, becomes necrotic, and ulcerates, leaving a back eschar surrounded by edema. Local lymphadenopathy, low-grade fever, and malaise are frequently found, but may not be present. Most cases are self-limiting; however, systemic antibiotic treatment is recommended to prevent the progression to a systemic disease. Diagnosis can be made by direct Gram-stain smear, culture, polymerase chain reaction, serology testing, or by the identification of spores in biopsy material. Treatment is typically with penicillin antibiotics or tetracyclines. Ciprofloxacin is recommended for prophylaxis if exposure is suspected. A killed anthrax vaccine is available that is effective in reducing the chance of developing the disease, but significant side effects prevent its widespread use on whole populations. Prevention is through livestock vaccination, reduction in soil contamination, decontamination of hides and wool, and early isolation and treatment of suspected cases (51-53).

Brucellosis

In production agriculture, farmers, veterinarians, abattoir workers, and meat packers are at risk. Brucella is a gram-negative bacterium with worldwide distribution. Three types exist: B. suis, found in pigs; B. abortus, found in cattle; and B. melitensis, found in sheep and goats. Infection is acquired by contact with contaminated animals or by ingesting infected milk or cheese (19,51).

Brucellosis begins as a febrile illness with malaise and weight loss. The most common findings are hepatomegaly, splenomegaly, lymphadenopathy, and osteoarticular involvement. Cutaneous manifestations are rare and nonspecific. Diagnosis is made by culture and serologic testing. Treatment is with doxycycline or rifampicin for 6 weeks. Prevention is through animal vaccination and control programs (51).

Erysipeloid (Fish-Handler's Disease)

Erysipeloid is found in hunters, fishermen, butchers, farmers, and poultry dressers. The infection is caused by the gram-positive bacterium Erysipelothrix rhusiopathiae, which infects fish, shellfish, mammals, and poultry. Most cases consist of a localized, bright red, well-demarcated cutaneous infection, most often involving the hands. A diffuse cutaneous form as well as a systemic infection with septicemia and endocarditis can also occur. The diagnosis requires a culture of the skin. In septicemia, blood cultures may be positive. Most cutaneous infections are self-limiting. Treatment is recommended to reduce the risk of septicemia and endocarditis. The penicillins and cephalosporins are the first-line treatment. Prevention is achieved through strict hygiene of work environments (51,54).

Fish Tank Granuloma

Mycobacterium marinum is an acid-fast, nontuberculous mycobacterium that causes a cutaneous lesion on traumatized skin following exposure to contaminated water. People who work in fisheries are most at risk. The most common source is fish tank exposure. Most cases are a red, painless papule at the site of inoculation that may become verrucous or ulcerated. The diagnosis is made by culture. Most cutaneous infections are self-limiting; rifampicin, minocycline, clarithromycin, and ciprofloxacin are the drugs most commonly prescribed. Prevention is achieved through hygiene and the use of disinfectants (50,51,54).

Rickettsial Infections

Rickettsia are obligate intracellular microorganisms that multiply within the endothelial cell cytoplasm. Most are transmitted by blood-sucking insects and mites and affect farmers, trappers, and hunters (51).

Marine (endemic) typhus is caused by Rickets typhus and is transmitted by rat and cat fleas. A fever, headache, and a generalized, erythemic papular rash develop. Antibiotics shorten the duration of the illness. Scrub typhus is caused by Orientia tsutsugamushi and is transmitted by mites that live on field rodents. A fever, eschar, lymphadenopathy, hepatosplenomegaly, and an ery-themic, evanescent rash occur. It is potentially fatal without treatment. Rocky Mountain spotted fever is caused by Rickettsia rickettsii and infects humans through ticks. It causes fever, malaise, headache, gastrointestinal bleeding, and a petechial rash. It can be fatal without treatment. Malaysian rubber estate workers have tested for antibodies against R. typhi, O. tsutsug-amushi, and TT 118 spotted fever group rickettsiae, presumably due to the large number of rats and rodents that live in the groves (51).

Diagnosis of Rickettsia infections is through the typical clinical presentation or indirect immunofluorescence antibody testing. Treatment is with doxycycline, tetracycline, or chloramphenicol (51).

Viral Infections Of

Orf (ecthyma contagiosum), caused by a paravaccinia subgroup of poxviruses that commonly infects sheep and goats, is common among veterinarians, farmers, and sheep herders. Transmission occurs through contact between the broken skin of humans and the pustular dermatitis that develops around the mouth and feet of infected animals. The infection begins with a red papule with surrounding erythema, which sometimes ulcerates before resolving. The first infection results in lifelong immunity. The problem is commonly self-diagnosed and underreported, and resolves spontaneously without treatment. Diagnosis is confirmed by viral culture, electron microscopy, and polymerase chain reaction (PCR) (51).

Human Papilloma Virus (HPV)

The wart causing HPV-7 is responsible for "butchers' wart" found in butchers, meat handlers, and fish handlers. Risk factors include trauma, low working temperatures, and humidity. It is thought to be due to the exposure of skin to infected meat and fish. Diagnosis can be confirmed by histology and is prevented by protective gloves and automated processing equipment. While the warts eventually spontaneously resolve, they can be unsightly, and peri-ungal warts can be painful. Treatment includes salicylic acid-based topical plasters or paints, tape occlusion, and cryotherapy (51).

Milker's Nodules

Milker's nodules are caused by the infection of dairy workers and veterinarians by a paravaccinia virus that is transmitted by direct contact from infected cow's udders to humans. The painful nodules that develop resemble orf and become crusted and resolve. Erythema multiforme and erythema nodosum can sometimes occur as secondary eruptions. Diagnosis can be confirmed by viral culture or histology. The use of gloves and automatic milking machines has made this disease less common in countries where such equipment is used (51).

Fungal Infections Dermatophytosis (Barn Itch)

A dermatophyte fungus can penetrate the keratinized layer of the skin, hair, and nails. The most common features of the fungous infection are scaling and erythema of the skin. In hairy areas, alopecia can develop. Inflammatory changes with boggy swelling and pruritus (kerion) can occur, especially on the scalp and beard. The diagnosis is made by Wood's light, KOH preparations under microscopy, and fungal cultures (55).

Miscellaneous Fungal Infections

Tinea pedis is common to farmers where their feet are exposed to humid or wet environments without protective boots. Treatment is with topical or oral antifungal agents. Animals can infect humans with dermatophytes. Tri-chophyton verrucosum infects cattle, horses, sheep, goats, dogs, donkeys, farm buildings and straw; T. mentagrophytes can be transmitted by cattle and domestic animals; Microsporum canis is common in domestic animals, especially cats; and M. nanum infects pigs. M. gypseum infects soil, leading to infection in unprotected farmers (51,55).

Parasitic Infections Scabies

Common to medical personnel, home care workers, and sex workers, scabies is also common to people who live in rural areas and practice poor hygiene. The mite Sarcoptes scabiei burrows into skin causing papules, eczematous rashes, and excoriations. The disease is often confused by agricultural workers with rashes due to pesticides and other chemicals. The diagnosis is by visualization of eggs and parts of the mite on a KOH preparation. Treatment with a topical permethrin treatment is usually curative, although more than one treatment may be necessary (19).

Protozoa

Mucocutaneous leishmaniasis is transmitted by sand flies and is endemic in tropical regions. It presents as a chronic, nonhealing nodular ulcer with an acral distribution. Diagnosis is made by smear microscopy, culture, histology, and PCR. Uncomplicated, localized cutaneous leishmaniasis can be left to heal spontaneously. Severe, disfiguring, and nonhealing lesions should be treated. Pentavalent drugs are commonly used (19,51).

Helminths

Larva Migrans

Larva migrans, called creeping eruption in England and by various other names in other countries, is caused by various animal nematodes, the most common being the hookworm Ancylostoma braziliense. These nematodes live in the intestines of cats, dogs, and other similar animals. Their ova are released in the animal's feces, where they hatch to form infective larvae. Transmission to humans occurs when contact is made with contaminated soil, particularly sandy beaches (19,51).

The larvae penetrate intact skin and produce a serpiginous, cutaneous eruption that is pruritic and can be observed to progress at up to 1 cm a day. Complications include impetigo and, rarely, Loeffler's syndrome. Treatment includes topical or oral thiabendazole, cryotherapy, albendazole, or iver-mectin. Preventive measures include wearing proper footwear and treating household and farm animals (19,51).

Cercarial Dermatitis

Called swimmer's itch in England and by other names in the water-rich countries where it is found, cercarial dermatitis is caused by the cercariae of trematodes (Schistosoma and Trichobilharzia) that live in fresh and salt water. Their primary hosts are water birds that release ova in their feces. These ova hatch into larvae that infect water snails. Under optimal conditions of sunlight and temperature, thousands of cercariae are released and reinfect more water birds. When the cercariae penetrate human skin, they die in the epidermis within a few hours. A monomorphic, pruritic, maculopapular skin eruption follows mainly on exposed skin. Treatment is symptomatic. Paddy field, pond, and aquarium workers are at risk (19,51).